Loft conversion timber sizes for Ashlar wall and collars

hi I am completing a Diy loft conversion. Steels are in which are uc71 203x203. All BC drawings and planning are approved and I've started. Our BC drawings are not very detailed on the above sizes. The structural engineer drawings only stated beam sizes and rafter sizes.

I've so many problems with both that I don't want to go back to them anymore and I'm just after the recommendations for timber sizes. The roof rafters are 100 x 50 and at 400 centres. There is 15 wall to wall. The engineer drawings specify all rafters at 100 x 50, would this include Ashlar and collars too? As I need to put in a timber to the I section of the rsj, a 175mm timber would be fine and I was just going to to order a job lot of this size and build the Ashlar using the same and collars. There is no ridge beam just the two floor beams to take weight of roof and new floor.

Are 175's over kill or OK please.

Thanks

 

Hi I'm not sure on the beam I left that to the structure engineer it's a massive rsj 206mm wide by 216 depth and the steel is 17mm thick top and bottom and 12 mm thick on the i section. It's in now too!

 

The SE had specified the rafters from Ashlar to collar but not those two!

I assume as dead weight on Ashlar then depth should be ok with anything 100mm and above. I just don't want to add weight with oversized timbers!

Thanks

 

Hi yes engineer said 100x50 and I've gone for c24 as this is what he said but my SE said c16! He has signed off my steels now and said he wants the back of joist hangers with an infill within the rsj and must be Bolted through the rsj and then the Ashlar wall plate strapped to the front of the rsj to wood infill.

My only question now is the rsj is 210 wide and ideally the Ashlar wall needs to be on the front edge as the floor sits lower than the beam. I'm waiting to hear from him if he is happy with that as I assume the roof load is then not dead centre of the beam!

 

The drawing is exactly what I've done.

Still waiting to hear from BC as I had asked him directly the question but if you've got this drawing from your SE then sounds as though it's fine.

Floor joists I'm going for a Wolfe system which are stronger and lighter than standard SC4 timbers as my span is 4.4m. I'm waiting on a quote.

The only drawback is I will need to overlap the ceilings with9.5mm plasterboard to fire rate the ceiling below as the wolf system would not give as much fire rating as an SC4 big heavy timber.

What about you?

The picture of what to end up with is what mine will look like apart from I've got a 175x47mm wall plate on the beam which the BC saw and was fine with.

 

I'll take a look tonight at those. BC came back and said sitting at front is fine as minimal twist providing rsj finally bricked in.

Our BC is helpful so far, I think they like you asking questions to confirm its all ok, personally if you're a competent person the finish will be better as well spend time on things and not bang them out like some Biulders. I had a new porch built and the brick work is very messy! Urggg

Keep in rich then in case any questions we both have! This weeken

By the way it was BC who said to me to add 9.5mm to existing ceiling if I'm not going for a solid timber.